In a communication network it is desirable to provide conference arrangements whereby many customers can be bridged together on a conference call. In the so-called "dial-up" conference arrangements, each conferee is summoned at the appropriate time by establishing a communication path to the customer station. The customer is informed that he or she is wanted for a conference call and then added to the conference bridge where the customer can talk with the other conferees on the bridge.
When dial-up type conference arrangements are under the control of an operator, the operator's position can be furnished with supervisory equipment to permit the operator to monitor continuously the status of each conference leg on the bridge in order to ascertain when a conferee answers, disconnects or is added to the bridge. Thus, the operator can inform the conferees on a conference when a party is to be added to or disconnected from the bridge.
If the conference is to be controlled from a customer station, it is generally not practical to provide each customer station with a supervisory capability similar to that of an operator's position.
Accordingly, without such supervisory capability, if a conferee inadvertently disconnects or the connection to the conferee's station is interrupted by an equipment failure, the absence of that conferee might go unnoticed by the remaining conferees.
In one known prior art arrangement, whenever a conferee disconnected from a conference, the conferees remaining on the bridge would hear a warning tone indicating that someone had left the conference. If the disconnect was unexpected the host of the conference would leave the conference and an announcement was played to the host informing the host of the directory number of the conferee that disconnected. The host could then enter an abbreviated code causing the automatic redialing of that directory number and the reconnection of the dropped conference leg.
While this arrangement was wholly suitable for its intended purpose, the arrangement lacked certain features. For example, if several conferees disconnected at the same time, it was difficult for the host to discern which conferee leg was inadvertently disconnected and which leg disconnected on purpose. Thus, the dialing of the abbreviated code may cause the wrong leg to be reconnected.
In addition, certain conferees that are served by a private branch exchange without the direct-inward-dialing feature, do not have individual directory numbers for each of their stations. These conferees are accessed by dialing the main directory number of the private branch exchange and asking the PBX attendant for the specific conferee by name of extension number. Consequently, on a customer originated dial-up conference the host has difficulty distinguishing between a plurality of conference legs that are accessed by the same private branch exchange directory number making it difficult to perform such tasks as transferring control of the conference to one of these legs, putting the leg in a privacy mode, etc.